1. Field of the Invention
The present invention relates to columnar sintered hydroxy-apatite, which has at least one capillary tube passed therethrough in the vertical direction, designed to be used as an osteofiller.
2. Description of the Prior Art
Biomaterials used for artificial bones and teeth are required to possess bioaffinity and suitable mechanical strength. In recent years, ceramics such as alumina, porcelain and hydroxy-apatite have come to be used as the fillers for man-made roots and osteo-lesions. Among these materials, hydroxy-apatite is the main constituent of bone and is a highly suitable material since it is characterized by bonding directly to bone and by adapting itself to biotissues. For instance, when an osteo-lesion is filled with porous hydroxy-apatite granules obtained by forming hydroxy-apatite heat treated with aqueous hydrogen peroxide and sintering the formed body at 1200.degree. C., neoplastic bone is observed over the entire region of the filled, porous hydroxy-apatite granules as well as in the micropores thereof. However, it has been reported that when densified hydroxy-apatite granules are filled in place, neoplastic bone is formed only in the marginal area of the filled region, and no neoplastic bone is found in the central area thereof. This indicates that the porous hydroxy-apatite is superior to the densified hydroxy-apatite with regard to the formation of neoplastic bone. It is also recognized that the same holds for hydroxy-apatite blocks. However, the porous hydroxy-apatite blocks used are reported to have a mechanical strength (compressive strength) of 173.1 kg/cm.sup.2 (at a microporosity of 55%) and 313.9 kg/cm.sup.2 (at a microporosity of 35%). Thus, mechanical strength is low. It is generally known that sintering increases the mechanical strength of powder aggregates but decreases the entire surface area, microporosity and water absorption thereof. If the hydroxy-apatite, which is a material high in bioaffinity, is sintered at elevated temperatures with a view to attaining sufficient mechanical strength, then its bioaffinity is lost due to a decrease in microporosity. Thus, a problem with the development of osteofillers of hydroxy-apatite is obtaining a sintered body excelling in both bioaffinity and mechanical strength. In order to solve this problem, various investigations have been made concerning improvements in a sintering process wherein sintering is carried out by hot isotropic pressing following pre-sintering at normal pressure; the addition of binders to decrease sintering temperature such as phosphates of strontium, calcium and barium, bioactive glass and nitrogenous glass; the use of sintered substrates such as sintered titanium/apatite combinations, forsterite, densified apatite and zirconia, which are applied to the surfaces with hydroxy-apatite; the impregnation of porous ceramics with calcium and phosphoric ions; and the sintering of filled hydroxy-apatite. Even now, however, densified and porous hydroxy-apatites are selectively used depending upon the particular purpose. That is, the former is used as an osteofiller for a site on which a force is applied, and the latter as an osteofiller for a site on which no force is applied.